[base] Apply BindOnceRewriter in //mojo

This change applies the BindOnceRewriter in //mojo.
This rewriter replaces calls to base::Bind and base::BindRepeating with
calls to base::BindOnce, in case the result is immediately assigned to a
base::OnceCallback. Given that base::RepeatingCallback is implicitly
convertible to base::OnceCallback, there is no change in functionality.

Steps:
  1. run_tool.py --tool base_bind_rewriters \
                 --tool-arg='--rewriter=bind_to_bind_once'
  2. git cl format

This CL was uploaded by git cl split.

R=sky@chromium.org

Bug: 714018
Change-Id: Iad24325ddf3b59c0f89c48cb3549331fc8ac3495
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2132395
Auto-Submit: Jan Wilken Dörrie <jdoerrie@chromium.org>
Commit-Queue: Scott Violet <sky@chromium.org>
Reviewed-by: Scott Violet <sky@chromium.org>
Cr-Commit-Position: refs/heads/master@{#760502}

mojo/core/mojo_core.cc

@@ -31,8 +31,8 @@ class IPCSupport {
   ~IPCSupport() {
     base::WaitableEvent wait(base::WaitableEvent::ResetPolicy::MANUAL,
                              base::WaitableEvent::InitialState::NOT_SIGNALED);
-    mojo::core::Core::Get()->RequestShutdown(base::BindRepeating(
-        &base::WaitableEvent::Signal, base::Unretained(&wait)));
+    mojo::core::Core::Get()->RequestShutdown(
+        base::BindOnce(&base::WaitableEvent::Signal, base::Unretained(&wait)));
     wait.Wait();
   }